Photoelectric conversion element

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nonmonocrystalline photoelectric conversion element having an improved lower conductive layer surface configuration, i-layer crystal structure, and doped layer structure.

2. Related Background Art

Increase in photoelectric conversion efficiency and improvement in optical degradation have been studied heretofore for the photoelectric conversion elements incorporating the pin junction of a nonmonocrystalline semiconductor.

It is known that increasing a concentration of dopant in a doped layer decreases activation energy of the doped layer, thereby increasing the built-in potential of the pin junction and the open-circuit voltage of the element.

It is also known that use of a microcrystalline material for the i-type semiconductor layer improves optical degradation.

It is reported that a solar cell using microcrystalline silicon (μ c-Si) achieved a photoelectric conversion efficiency of 4.6% using plasma enhanced CVD using VHF (70 MHz) and that the solar cell demonstrated no optical degradation at all, as seen in J. Meier, A. Shah, “INTRINSIC MICROCRYSTALLINE (μ c-Si:H)-A PROMISING NEW THIN FILM SOLAR CELL MATERIAL,” IEEE WCPEC; 1994 Hawaii, p.409. Further, a stacked solar cell was fabricated by combining of amorphous silicon with microcrystalline silicon and achieved an initial photoelectric conversion efficiency of 9.1%.

It is also known that a transparent, conductive layer is interposed between the substrate or metal layer and the semiconductor layers. This prevents elements in the metal layer from diffusing or migrating into the semiconductor layers, thus preventing the photoelectric conversion element from shunting. Further, it has a moderate resistance and prevents the semiconductor layers from short-circuiting due to a defect such as a pinhole. In addition, the transparent, conductive layer is provided with an uneven surface, thereby increasing irregular reflection of incident light and reflected light to lengthen optical pathlengths in the semiconductor layers.

With the above-stated solar cell using the microcrystalline silicon based material, however, the photoelectric conversion efficiency thereof is still too low, 4.6%, to be of practical use.

With the stacked solar cell of a-Si/μ c-Si, the initial photoelectric conversion efficiency is as high as 9.1%, but it suffers from great optical degradation of the a-Si layer on the light incidence side. Further, the thickness of the μ c-Si layer is thick, 3.6 μm, and the rate of deposition is slow, 1.2 Å/sec. Thus, the time necessary for layer formation is approximately eight hours; this poses another problem in that the time for layer formation does not reach an industrially practical level.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a photoelectric conversion element having a substrate, a lower conductive layer, a first doped layer, an ilayer, a second doped layer, and an upper conductive layer, wherein a surface of the lower conductive layer has an uneven configuration, the i-layer contains prismatic crystalline grains, and longitudinal directions of the prismatic crystalline grains are inclined with respect to a direction of a normal line to the substrate. According to an embodiment of the present invention, as a numerical definition, a percentage of an overall volume of prismatic crystalline grains, each having a below-defined angle of 20° or less, is 70% or more with respect to an overall volume of the i-layer; the angle is defined as an angle between a straight line A passing a prismatic crystalline grain and being parallel to a longitudinal direction thereof and a straight line B passing the prismatic crystalline grain A out of straight lines taking shortest courses between interface

1

between the first doped layer and the i-layer and interface

2

between the second doped layer and the i-layer.

Further, according to another embodiment, the photoelectric conversion element is characterized in that a third doped layer, a second i-layer, and a fourth doped layer are interposed between the second doped layer and the upper conductive layer, the second i-layer has an amorphous silicon based semiconductor, and a thickness of the second i-layer is in the range of 0.1 μm to 0.4 μm both inclusive.

According to the present invention, the photoelectric conversion element is characterized in that the first doped layer and/or the third doped layer is of a stacked structure comprising a layer of a microcrystalline silicon based semiconductor material and a layer of an amorphous silicon based semiconductor material and in that the layer of the microcrystalline silicon based semiconductor material is in contact with the i-layer.

The photoelectric conversion element of the present invention is improved in characteristics including photoelectric conversion efficiency, open-circuit voltage, short-circuit photocurrent, low-illuminance open-circuit voltage, and leak current of the photoelectric conversion element. In addition, durability of the element is enhanced in outdoor exposure tests, in mechanical strength tests, and upon long-term irradiation with light. Further, the cost of a photoelectric conversion element can be decreased greatly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B

are drawings to show photoelectric conversion elements of the present invention featuring the lower conductive layer and the i-layer;

FIG. 2

is a drawing to show a conventional photoelectric conversion element;

FIG. 3

is a drawing to show an example of a collector electrode;

FIGS. 4A and 4B

are drawings to show an example of a photoelectric conversion element module according to the present invention;

FIG. 5

is a drawing to show a photoelectric conversion element of the present invention featuring the first doped layer;

FIG. 6

is a drawing to show the relationship between surface roughness of the lower conductive layer and photoelectric conversion efficiency;

FIG. 7

is a drawing to show the relationship between photoelectric conversion efficiency and percentage of angle G defined in

FIG. 1A

in the range of 15° to 45° both inclusive;

FIG. 8

is a drawing to show an apparatus for forming the lower conductive layer and upper transparent electrode of the photoelectric conversion element of the present invention;

FIG. 9

is a drawing to show an apparatus for forming the photovoltaic layer of the photoelectric conversion element of the present invention;

FIG. 10

is a drawing to show an apparatus for continuously forming the lower conductive layer and upper transparent electrode of the photoelectric conversion element of the present invention;

FIG. 11

is a drawing to show an apparatus for continuously forming the photovoltaic layer of the photoelectric conversion element of the present invention;

FIG. 12A

is a drawing to show the relationship of photoelectric conversion efficiency with percentage of angle F defined in

FIG. 12B

in the range of 0° to 20° both inclusive;

FIG. 12B

is a drawing for defining angle F; and

FIG. 13

is an example of the photoelectric conversion element of the present invention provided with bus-bars.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A

is a schematic, cross-sectional view of the photoelectric conversion element of the present invention, wherein reference numeral

101

designates a substrate,

102

a lower conductive layer comprised of two layers, reflecting layer

102

a

and transparent, conductive layer

102

b

,

103

a first doped layer of a nonmonocrystalline silicon based semiconductor material,

104

a layer of a microcrystalline silicon based semiconductor material having the i-type conduction property, and

105

a layer of a nonmonocrystalline silicon based semiconductor material having the opposite conduction property to that of the first doped layer. The layer structure of

103

-

104

-

105

forms the p-i-n junction and generates photoelectromotive force. The layers

103

,

104

,

105

will be referred to together as a photovoltaic layer. Numeral

106

denotes an upper transparent electrode and

107

a collector electrode.

The lower conductive layer

102

, i-layer

104

, and first doped layer

103

of the present invention have the following features.

(1) The relationship of mechanical strength and photoelectric conversion efficiency to the direction of prismatic crystalline grain was checked. Frequency distribution of angle F between straight line A passing a certain prismatic crystalline grain A and being parallel to the longitudinal direction thereof and straight line B passing the prismatic crystalline grain A out of straight lines taking shortest courses between interface

1

between the first doped layer and the first i-layer and interface

2

between the second doped layer and the first i-layer, was checked as shown in FIG.

12

B. Then the relation of photoelectric conversion efficiency after a “torsion test” to the percentage K of overall volume of prismatic crystalline grains, each having an angle F of 20° or less, with respect to the overall volume of the first i-layer was checked. The result is shown in FIG.

12

A. It was found that when the percentage K was 70% or more, good photoelectric conversion efficiencies were presented and that when the percentage K was less than 70%, the open-circuit voltages were decreased and the photoelectric conversion efficiencies were lowered. The “torsion test” was conducted in compliance with JIS C8917 A-10 for a crystalline solar cell. Conditions were such that torsion of height h=5 mm was repetitively given fifty times for the area of 10 cm×10 cm.

(2) The lower conductive layer

102

of the present invention was made so that surface roughness Ra in the length of about several ten micrometers of the surface thereof was in the range of 0.1 μm to 1 μm inclusive. Then, (surface roughness)×(refractive index of the first i-layer) becomes nearly equal to the wavelengths of visible light or infrared light, and the optical confinement effect is thus demonstrated, thereby remarkably increasing the short-circuit photocurrent of the photoelectric conversion element.

Long-wavelength light not absorbed inside the first i-layer is reflected by the lower conductive layer, and the reflected light is again incident into the i-layer. Since the light is scattered by the surface of the lower conductive layer, it does not undergo interference inside the i-layer, and there is no region strongly absorbing the light. Thus, the optical degradation can be suppressed further. Similarly, a region absorbing only a little light is absent, and the open-circuit voltage can thus be increased.

The relationship was checked between surface roughness and photoelectric conversion efficiency. The results are shown in FIG.

6

. It was proved that excellent conversion efficiencies were shown in the above-stated range of surface roughness.

(3) When regions wherein angle G between a normal line to the surface of the lower conductive layer in a fine area of approximately several hundred Å and a normal line to the principal plane of a substrate is between 15° and 45° both inclusive are 80% or more of the total surface region, thickness distribution of the first i-layer is small, and only a small region having an extremely small thickness is present. Thus, the leak current is small, and the open-circuit voltage can be increased. In addition, the optical confinement effect is further enhanced.

The relationship was checked between photoelectric conversion characteristics of a solar cell after the “torsion test” and distribution of an angle (angle G) made between the normal line to the fine area of the lower conductive layer and the normal line to the principal plane of the substrate. The angle G is illustrated in FIG.

1

A.

FIG. 7

shows the relationship of the above angle G to photoelectric conversion efficiency after the “torsion test.” It was found that when the percentage of angle G was 80% or less, the shunt resistance was lowered (weak short-circuit condition), thereby lowering the photoelectric conversion efficiency.

(4) Photocarriers generated in the i-layer migrate because of an internal electric field, and the internal electric field is nearly parallel to straight lines taking shortest courses between the first doped layer and the second doped layer. Therefore, in the present invention, longitudinal directions of prismatic crystalline grains contained in the i-layer are made nearly parallel to the straight lines taking the shortest courses between the first doped layer and the second doped layer, and lengths of the prismatic crystalline grains in the longitudinal direction are determined between 100 Å and 0.3 μm inclusive, which decreases chances of passage of carriers through interfaces present between crystal grains, thereby increasing the fill factor and short-circuit current.

Since the chances of passage of carriers through the interfaces are decreased, a rate of recombination of carriers can be decreased. Accordingly, optical degradation can be suppressed further. Since directions of prismatic crystalline grains are almost aligned, the interface state density of prismatic crystalline grains is small. Therefore, the open-circuit voltage can be increased.

Further, an absorption coefficient of light is higher than that of monocrystalline silicon and an absorption coefficient of long-wavelength light is higher than those of amorphous silicon based semiconductor materials. Therefore, the light is effectively absorbed up to the long wavelengths (infrared light), and sufficient short-circuit current can be obtained even in the thickness of about 3 μm.

Since an area between prismatic crystalline grains is occupied by the good amorphous silicon based semiconductor material containing hydrogen, the probability that photocarriers will be trapped in this area is almost zero.

As a whole, the most longitudinal directions of prismatic crystalline grains have angles in the range of 10° to 50° both inclusive with respect to the normal line to the principal plane of the substrate, and they can thus relax external torsion or the like. Therefore, separation of film will not occur when a long substrate is wound around a roll in carrying out the roll-to-roll method. Since film separation does not occur, the photoelectric conversion element can be formed even on a curved substrate. Similarly, it is also easy to use the photoelectric conversion element of the present invention formed on a flat substrate in a curved state. Particularly, when the photoelectric conversion element of the present invention is used as a solar cell, it can also be used on a curved surface such as a building wall.

Additionally, since the short-circuit current can be increased as described above, the first i-layer can be formed in a smaller thickness, which can improve optical degradation, increase productivity, and decrease power cost.

(5) Another feature is that in the i-layer, fine areas of the amorphous silicon based semiconductor material exist at a volume percentage of 50% or less with respect to the overall region of the i-layer. This can make the open-circuit voltage higher than that of the photoelectric conversion element in which the entirety of the first i-layer is made of the microcrystalline silicon based semiconductor material.

Although the reason is not clear, the leak current can be decreased, so that the open-circuit voltage can be made higher. Further, the strength against external force becomes higher than that of the photoelectric conversion element in which the entirety of the first i-layer is made of the microcrystalline silicon based semiconductor material. Since the flexibility of the Si—Si—network of in the amorphous silicon based material is higher than that of in the microcrystalline silicon based material, the areas of the amorphous silicon based semiconductor material contained in the first i-layer are considered to be effective upon relaxation of external force. Further, they are also considered to be similarly effective upon relaxation of internal stress.

Since the optical degradation becomes unignorably prominent at volume percentages of 50% and more, a desired element structure is the stacked having the structure of a-Si/μ c-Si, for example.

(6) The stacked cell as shown in

FIG. 1B

is characterized in that third doped layer

110

, second i-layer

111

, and fourth doped layer

112

are successively stacked on the above-stated pin junction

103

to

105

and in that the thickness of the second i-layer

111

is in the range of 0.1 μm to 0.4 μm both inclusive. Spectral sensitivity to light can be increased in a wider wavelength region by making the second i-layer of a semiconductor material with a larger light absorption coefficient of short-wavelength light, e.g. a-Si, and making the first i-layer of a semiconductor material with a larger light absorption coefficient of long-wavelength light, e.g., μ c-Si, in this order from the light incidence side as described.

Further, the open-circuit voltage can be made higher than that of the photoelectric conversion element wherein the first i-layer is made of μ c-Si, which can increase the photoelectric conversion efficiency. Since the second i-layer of μ c-Si can be made in a smaller thickness by connecting the i-layers of different spectral sensitivities as described above, the fill factor (FF) of the photoconductive characteristic can be improved.

Since the thickness of the second i-layer of the present invention is thin, between 0.1 μm and 0.4 μm both inclusive, as much optical degradation can be suppressed as possible, even if amorphous semiconductor is used for the second i-layer.

Further, though the reason is indefinite, the leak current of the photoelectric conversion element can be decreased by stacking of the second i-layer of amorphous silicon based semiconductor material. Therefore, the open-circuit voltage can be increased further.

Particularly, when the photoelectric conversion element of the present invention is used as a photosensor or as an image sensor, the decrease of leak current is important. When the photoelectric conversion element of the present invention is used as a solar cell, it can output a high open-circuit voltage even under low light illumination. For example, no extreme drop of power generation efficiency will take place even on a cloudy day or during a time near dawn or dusk.

Since the lower conductive layer is not flat as described above, the light does not interfere inside the second i-layer. Therefore, there is no region strongly absorbing the light, and the optical degradation can be suppressed further. Since the region absorbing only a little light is absent similarly, the open-circuit voltage can be increased.

(7) Method for forming the first i-layer

The i-layer

104

is characterized by being formed by plasma enhanced CVD using an electromagnetic wave having a frequency in the range of 30 MHz to 600 MHz both inclusive and under such conditions that the pressure is between 1 mTorr and 1 Torr both inclusive, hydrogen gas and a gas containing silicon are used as source gases, and a percentage of the gas containing silicon to the hydrogen gas is in the range of 0.5% to 30% both inclusive.

Since the plasma enhanced CVD using the electromagnetic wave having the frequency in the above range can induce the plasma at lower pressure than RF (13.56 MHz industrially applied) plasma enhanced CVD, it is free from the generation of polysilane in vapor phase and can thus make the microcrystalline silicon based semiconductor material with high quality.

Since the plasma can be induced at low pressure, the plasma can be expanded, which is very suitable for the fabrication of a large-area photoelectric conversion element. For these reasons, the rate of deposition can be increased, and the throughput is increased thereby, which is industrially advantageous. Since the gas containing silicon is diluted with a large amount of hydrogen gas, a larger amount of radicals containing hydrogen can be supplied to the surface for a film to be formed thereon than in normally forming the thin film of amorphous silicon based semiconductor, so that the microcrystalline silicon based semiconductor thin film can be formed with good quality.

Since a negative self-bias normally appears at the electrode for discharge, positive ion species with high energy can be prevented from hitting the surface for the film to be formed thereon, so that the microcrystalline silicon based semiconductor thin film can be formed with good quality.

Although the reason is not yet clear, the microcrystalline structure according to the present invention can be made with good reproducibility by the method described above. Since the above method has higher gas decomposition efficiency than the RF plasma enhanced CVD process, it shows excellent gas use efficiency, thus being industrially advantageous.

(8) Method for forming the second i-layer

The material for the second i-layer is selected from amorphous silicon based semiconductor materials, specific examples of which are a-Si, a-SiC, and a-SiO. Particularly, a-Si is excellent. For making the i-layer more intrinsic, B may be added, for example. A concentration of H, Cl, and F atoms for compensating for unbound bonds (dangling bonds) is preferably between 0.1% and 10% both inclusive. A method for forming this layer is one of the ordinary plasma enhanced CVD processes. Among such processes, RF plasma enhanced CVD is preferred. The rate of deposition is preferably between 1 Å/sec and 20 Å/sec both inclusive, the temperature of formation is preferably between 150° C. and 350° C. both inclusive, and the pressure is preferably between 0.1 Torr and 5 Torr both inclusive. Particularly, in making the second i-layer of microcrystalline structure, the doped layer is made preferably under such conditions that hydrogen gas and a gas containing silicon are used as source gases, and a percentage of the gas containing silicon to the hydrogen gas is between 2% and 50% both inclusive.

(9) Another feature is such that at least one layer of the first doped layer

103

, the second doped layer

105

, the third doped layer

110

, and the fourth doped layer

112

is made of a microcrystalline silicon based semiconductor material.

Since use of the microcrystalline silicon based semiconductor material for the doped layer can increase the carrier density of the layer, the open-circuit voltage of the photoelectric conversion element is increased. Further, since the microcrystalline silicon based semiconductor material has a smaller absorption coefficient in the visible light region than the amorphous silicon based semiconductor materials, it increases the short-circuit current when used for the window layer on the light incidence side.

Yet further, when the microcrystalline silicon based semiconductor material is used for the first doped layer

103

and the second doped layer

105

, the interface state density is small, because there is no sudden change at the interface to the first i-layer

104

. Thus, the fill factor of the photoconductive characteristic is increased.

(10) As shown in

FIG. 5

, the first doped layer is preferably made in a stacked structure comprised of a layer (

503

a

) of an amorphous silicon based semiconductor material on the lower conductive layer side and a layer (

503

b

) of a microcrystalline silicon based semiconductor material on the first i-layer side. The third doped layer may be constructed of the same structure. This application of the stacked structure to the doped layer can improve the fill factor of a photoelectric conversion element.

For forming the microcrystalline silicon based semiconductor material, a large amount of hydrogen gas is often made to flow in the plasma. In that case, for example, when tin oxide is used for the lower conductive layer, the tin oxide will be reduced, which could result in the failure to form a good semiconductor junction.

(11) Method for forming the transparent, conductive layer of the present invention.

The transparent, conductive layer is made of a material selected from zinc oxide, tin oxide, indium oxide, ITO, and zinc sulfide. The material is, however, preferably zinc oxide or tin oxide with regard to ease of surface configuration and the control.

The conductive layer is normally made at a deposition rate in the range of 10 (Å/sec) to 200 (Å/sec) both inclusive, using high deposition rate DC magnetron sputtering. In addition, it is important to make the layer at the temperature in the range of 100° C. to 500° C. both inclusive. Particularly, the temperature is preferably between 150° C. and 400° C. both inclusive. The transparent, conductive layer having the cross-sectional configuration as in the present invention can be obtained at the deposition rate and formation temperature described above, and the transmittance thereof is 90% or more for light of 500 nm and higher. After the layer is formed by the above method, the surface of the substrate may be etched moderately with an acid solution such as HNO

3

, HF, HCl, or H

2

SO

4

, to make the surface uneven.

The other components will be described.

Substrate

The substrate

101

is made of a material selected from metals, plastics, glass materials, ceramics, and bulk semiconductors. The surface of the substrate may have fine unevenness. The substrate having a long shape can be applied to continuous film formation. Particularly, stainless steel or polyimide is preferred, because they have flexibility.

Reflecting layer

The reflecting layer

102

a

functions as an electrode and as a reflecting layer for reflecting the light arriving at the substrate to allow the reflected light to be again utilized in the semiconductor layers. It is made by a method selected from vapor deposition, sputtering, plating, and printing of Al, Cu, Ag, or Au.

The surface has unevenness, which functions to lengthen optical pathlengths in the semiconductor layers of the reflected light and to increase the short-circuit current.

If the substrate is electrically conductive, the reflecting layer does not always have to be present.

Upper transparent electrode

If the thickness is properly set, the upper transparent electrode

106

can also serve as a reflection preventing layer.

The transparent electrode

106

is made by a method selected from vapor deposition, CVD, spraying, spin-on, and dipping with a material such as ITO, ZnO, or InO

3

. These compounds may contain a substance for changing electric conductivity.

Collector electrode

The collector electrode

107

is provided for increasing collection efficiency. A method for forming the collector electrode may be selected from a method for forming a metal electrode pattern by sputtering with a mask, a method of printing an electroconductive paste or a soldering paste, a method for bonding a metal wire with an electroconductive paste, and so on. An example using a copper wire is shown in

FIG. 3. A

silver cladding layer is made around a fine copper wire. This layer functions to reduce contact resistance with the copper wire. Further, a carbon layer with a binder of acrylic resin is made around the silver cladding layer. This layer functions to maintain adhesion to the upper transparent electrode and functions to reduce contact resistance with the silver cladding layer. It also functions to prevent silver in the silver cladding layer from diffusing into the photovoltaic layer.

Further, bus-bars, etc. for taking power out are formed as shown in

FIG. 13. A

plurality of collector electrodes are arranged without intersection on the surface of the element and one ends thereof are in electrical contact with the bus-bar

108

. The bus-bar

108

is formed on

107

and a metal material with high conductivity, such as a Cu plate, is used therefor. An electrically insulating, double-sided adhesive tape is interposed between the bus-bar and the upper transparent electrode to make the bus-bar adhere to the upper transparent electrode.

FIGS. 4A and 4B

show an example of a module of a photoelectric conversion element according to the present invention. As shown in

FIGS. 4A and 4B

, a plurality of photovoltaic elements are connected in series, and a bypass diode

406

is connected in parallel with each photoelectric conversion element. This is advantageous in that even if one photoelectric conversion element is shadowed, all voltages generated by the other photoelectric conversion elements can be prevented from being applied to the shadowed photoelectric conversion element. Since the photovoltaic module of the present invention is sealed by fluororesin and support substrate after placement of each member as shown in

FIGS. 4A and 4B

, it is free from intrusion of water vapor.

EXAMPLES

The present invention will be described in further detail with examples of solar cells as photoelectric conversion elements, but it is noted that the present invention is by no means intended to be limited to the examples.

Example 1

The solar cell of

FIG. 1A

having one pin junction was fabricated. Specifically, the solar cell comprised a stainless steel (SUS having an area of 10×10 cm

2

and a thickness of 0.2 mm)/a Ag reflecting layer a ZnO transparent, conductive layer a first doped layer of a-Si:H:P/a first i-layer of μ c-Si:H/a second doped layer of μ c-Si:H:B/an upper transparent electrode of ITO/a Cu collector electrode wire/Ag/material of C (FIG.

3

).

In this example, the transparent, conductive layer was made by sputtering using the apparatus of

FIG. 8

, the photovoltaic layer was made using the apparatus of

FIG. 9

, the first i-layer was made by plasma enhanced CVD using the high frequency of 500 MHz, the doped layers were made by RF plasma enhanced CVD, and the upper transparent electrode layer was made by sputtering.

Procedures for forming the lower conductive layer of the reflecting layer and the transparent, conductive layer by sputtering will be described.

FIG. 8

shows the apparatus that can carry out sputter etching and DC magnetron sputtering process, wherein reference numeral

801

designates a cylindrical deposition chamber,

802

a substrate holder,

803

the substrate,

804

a heater,

805

a matching box,

806

an RF power supply,

807

a metal target for formation of a reflecting layer,

808

a target for formation of transparent, conductive layer,

810

and

811

DC power supplies,

813

and

814

shutters,

816

an exhaust pipe,

817

a gas inlet pipe,

818

a rotary shaft, and

819

the plasma. In addition, there are a gas supply device connected to the gas inlet pipe

817

and a vacuum pump connected to the exhaust pipe

816

, though not illustrated. Numeral

821

represents an arrow indicating a direction of exhaust. First, the substrate

803

, cleaned with an acid and cleaned with an organic solution, is attached to the disk substrate holder, and the rotary shaft

818

being a center axis of this disk substrate holder is rotated. Then the inside of the deposition chamber is evacuated to a vacuum of 5×10

−6

Torr by use of an oil diffusion pump/rotary pump not illustrated. Then Ar is introduced through the gas inlet pipe, and the RF power is introduced from the RF power supply

806

to the inside of the deposition chamber, thereby inducing Ar plasma. The matching circuit

805

is adjusted so as to minimize reflected power. On this occasion, the substrate is sputter-etched (or reversely sputtered) to have a cleaner surface. Then the heater is set to achieve the temperature for formation of a reflecting layer. When the predetermined temperature is achieved, the DC power supply

810

is turned on to induce the Ar plasma

819

. Then the shutter

813

is opened. When the reflecting layer is made in a predetermined thickness, the shutter is closed and the DC power supply is turned off. Next, the heater is set so as to achieve the temperature for formation of a transparent, conductive layer. When the predetermined temperature is achieved, the DC power supply

811

is turned on to induce the Ar plasma. Then the shutter

814

is opened. After the transparent, conductive layer is made in a predetermined thickness, the shutter is closed and the DC power supply is turned off.

FIG. 9

shows the apparatus that can carry out the plasma enhanced CVD process, in which reference numeral

901

designates a reaction chamber,

902

the substrate on which the lower conductive layer was made,

903

a heater,

904

a conductance valve,

908

a high-frequency electrode,

909

a high-frequency power supply (500 MHz) having a built-in matching circuit,

910

the plasma,

911

a shutter,

914

an exhaust pipe, and

915

a gas inlet pipe. Numeral

913

denotes a direction of exhaust and

916

a gas introducing direction. Although not illustrated, the oil diffusion pump/vacuum pump such as the rotary pump are connected to the exhaust pipe of the drawing, and the gas supply device is connected to the gas inlet pipe as illustrated. The plasma enhanced CVD system is constructed as described above.

Actual layer formation is carried out as follows, using this plasma enhanced CVD system. First, the substrate

902

on which the lower conductive layer was made is attached to the heater

903

inside the reaction chamber

901

, and the inside of the reaction chamber is evacuated by the oil diffusion pump/the vacuum pump such as the rotary pump before the pressure inside the reaction chamber becomes 1×10

−4

Torr or less. When the pressure becomes 1×10

−4

Torr or less, a gas such as H

2

or He is introduced from the gas inlet pipe

915

into the reaction chamber, and the heater is powered so as to set the substrate

902

at a desired temperature. When the temperature of the substrate becomes stable, the source gas is introduced from the gas inlet pipe, and the high-frequency power supply

909

is turned on to introduce the high-frequency power from the high-frequency electrode

908

into the reaction chamber. When the plasma

910

is induced, the conductance valve

904

is adjusted to attain a desired pressure. On that occasion, the matching circuit is preferably adjusted to minimize reflected power. Then the shutter

911

is opened. When the layer is made in a desired thickness, the shutter is closed, and the introduction of high-frequency power and the introduction of source gas is stopped. Then preparation is made for formation of the next layer. If this apparatus is used with the RF plasma enhanced CVD process, the above high-frequency power supply

909

is replaced by the RF power supply (13.56 MHz) to introduce the RF power to induce the plasma.

Specific conditions are shown in Table 1A.

TABLE 1A

Temper-

ature

Thick

Layer

Material

(° C.)

(μm)

Gas

Method

Lower

reflecting

Ag

25

0.1

Ar

SP

conductive

layer

method

layer

transparent

ZnO

250

1.0

Ar

SP

conductive

method

layer

Ratio

Tem-

Power

of

per-

fre-

flow

Pres-

ature

Thick

quency

rates

sure

Layer

Material

(° C.)

(μm)

(MHz)

SiH

4

/H

2

(Torr)

Photo-

1st

a-Si:H:P

350

0.05

13.56

0.08

1.0

voltaic

doped

layer

layer

1st i-

μ c-Si:H

400

0.80

500

0.04

0.01

layer

2nd

μ c-

200

0.006

13.56

0.02

1.5

doped

Si:H:B

layer

Temper-

ature

Thick

Layer

Material

(° C.)

(μm)

Gas

Method

Upper electrode

ITO

160

0.08

Ar

SP method

SP method: sputtering

As shown in

FIG. 13

, the electrically insulating, double-sided adhesive tape was placed on one side of the substrate up to the upper transparent electrode (ITO), one end of collector electrodes each comprised of the Cu wire, Ag cladding layer, and carbon paste shown in

FIG. 3

are stuck to the double-sided adhesive tape, a bus-bar is stuck to the double-side adhesive tape from above the collector electrodes, and the whole is heated to fuse the carbon paste, thereby fixing the collector electrodes to the bus-bar.

Several solar cells (Ex. 1) were made in the same structure as above. The cross-sectional shape of one of them was observed by a transmission electron microscope (TEM), which indicated that the first i-layer was made in such structure that the longitudinal directions of prismatic crystalline grains are inclined with respect to the direction of the normal line to the substrate as shown in

FIG. 1A

or

1

B. The surface roughness Ra of the lower conductive layer (the transparent, conductive layer and the reflecting layer) was measured, which showed that an average per 50 μm length was 0.32 μm. A percentage of angles G (each of which is an angle between a normal line to a fine area of the lower conductive layer and the normal line to the principal plane of the substrate) in the range of 15° to 45° both inclusive was calculated, and the percentage was 91%. The percentage of the overall volume of prismatic crystalline grains, each having the angle F of 200 or less, was 92% with respect to the overall volume of the i-layer.

Comparative Example 1

The solar cell having the cross-sectional shape of

FIG. 2

was made in such structure that the lower conductive layer was an almost flat film of only Ag by the ordinary sputtering process without provision of the transparent, conductive layer. The first i-layer was made under the conditions shown in Table 1B by RF plasma enhanced CVD. The solar cell (the photoelectric conversion element of

FIG. 2

) was fabricated in the same manner as in Example 1 except for the above.

The conditions of formation are shown in Table 1B.

TABLE 1B

Temper-

ature

Thick

Layer

Material

(° C.)

(μm)

Gas

Method

Lower conductive

Ag

25

0.1

Ar

SP method

layer

Ratio

Tem-

Power

of

per-

fre-

flow

Pres-

ature

Thick

quency

rates

sure

Layer

Material

(° C.)

(μm)

(MHz)

SiH

4

/H

2

(Torr)

Photo-

1st

a-Si:H:P

350

0.05

13.56

0.08

1.0

voltaic

doped

layer

layer

1st i-

μ c-Si:H

400

0.80

13.56

0.03

1.2

layer

2nd

μ c-

200

0.006

13.56

0.02

1.5

doped

Si:H:B

layer

Temper-

ature

Thick

Layer

Material

(° C.)

(μm)

Gas

Method

Upper electrode

ITO

160

0.08

Ar

SP method

SP method: sputtering

Several solar cells (Comp. Ex. 1) were fabricated in the same structure. The cross-sectional shape of one of them was observed by the transmission electron microscope (TEM), which indicated that the first i-layer was made of prismatic microcrystalline silicon as shown in FIG.

2

. The surface roughness Ra of the lower conductive layer was measured, which showed that the average per 50 μm length was 0.02 μm.

First, the initial characteristics (photoconductive characteristic, leak current, and open-circuit voltage under low illuminance) were measured for the solar cells (Ex. 1) of Example 1 and the solar cells (Comp. Ex. 1) of Comparative Example 1.

The photoelectric conversion efficiency, the open-circuit voltage, and the short-circuit photocurrent were measured using a solar simulator (AM 1.5, 100 mW/cm

2

, surface temperature 25° C.), which confirmed that the photoelectric conversion elements of the present invention were 1.29 times, 1.04 times, and 1.23 times, respectively, better than those of the comparative example.

Next, the open-circuit voltage was measured under a fluorescent lamp (of low illuminance) of the approximately 500 lx illuminance, which showed that the solar cells of (Ex. 1) were 1.2 times better than those of (Comp. Ex. 1). The leak current was measured with a backward bias being applied at a dark place, which indicated that the leak currents of the solar cells (Ex. 1) of the present invention were about one eighth or so of those Comparative Example 1 (Comp. Ex. 1) and that the solar cells of the present invention were thus superior.

The light-soaking test was next conducted for the solar cells of Ex. 1 and Comp. Ex. 1. After exposure for 1000 hours to the above simulator (AM 1.5, 100 mW/cm

2

, surface temperature 50° C.), none exhibited a failure of appearance.

After the light-soaking test, the photoelectric conversion efficiency, open-circuit voltage, short-circuit photocurrent, open-circuit voltage under low illuminance, and leak current were measured, which showed that differences were observed in drops of the open-circuit voltage under low illuminance and the leak current before and after the test.

A ratio of open-circuit voltages under low illuminance before and after the test (low-illuminance open-circuit voltage after test/low-illuminance open-circuit voltage before test) was 0.95 for Ex. 1 or 0.92 for Comp. Ex. 1. Further, a ratio of leak currents before and after the test (leak current after test/leak current before test) was 1.2 for Ex. 1 or 2.2 for Comp. Ex. 1.

It was thus proved that the photoelectric conversion element of the present invention was better than the conventional photoelectric conversion element, as described above.

Further, the “torsion test” described previously was conducted. The two solar cells showed no failure of appearance after the test.

After the torsion test, the photoelectric conversion efficiency, open-circuit voltage, short-circuit photocurrent, open-circuit voltage under low illuminance, and leak current were measured, and differences were observed in drops of the photoelectric conversion efficiency, open-circuit voltage, open-circuit voltage under low illuminance, and leak current before and after the test.

A ratio of photoelectric conversion efficiencies before and after the test (photoelectric conversion efficiency after test/photoelectric conversion efficiency before test) was 0.98 for Ex. 1 or 0.93 for Comp. Ex. 1. A ratio of open-circuit voltages before and after the test (open-circuit voltage after test/open-circuit voltage before test) was 0.99 for Ex. 1 or 0.94 for Comp. Ex. 1.

The ratio of open-circuit voltages under low illuminance before and after the test (low-illuminance open-circuit voltage after test/low-illuminance open-circuit voltage before test) was 0.96 for Ex. 1 or 0.87 for Comp. Ex. 1. Further, the ratio of leak currents before and after the test (leak current after test/leak current before test) was 1.1 for Ex. 1 or 3.1 for Comp. Ex. 1.

It was proved that the photoelectric conversion element of the present invention was better than the conventional photoelectric conversion element, as described above.

Similarly, a hailstorm test was conducted according to JIS C 8917 related to the crystalline solar cells. Ice balls about 25 mm in diameter were dropped about ten times at a final velocity 23 m/sec. The same evaluations as described above were conducted after the test, which showed that the solar cells of Ex. 1 were better than those of Comp. Ex. 1.

Example 2

The solar cell of

FIG. 1B

was fabricated as another example. Specifically, several solar cells (Ex. 2) were made comprising a stainless steel substrate (SUS 430 having an area of 10×10 cm

2

and a thickness of 0.2 mm)/an Al reflecting layer a ZnO transparent, conductive layer a first doped layer of a-Si:H:P/a first i-layer of μ c-Si:H/a second doped layer of μ c-Si:H:B/a third doped layer of a-Si:H:P/a second i-layer of a-Si:H/a fourth doped layer of μ cSi:H:B/an upper transparent electrode of ITO/a Cu collector electrode wire/Ag/material of C.

The formation conditions are shown in Table 2.

TABLE 2

Temper-

ature

Thick

Layer

Material

(° C.)

(μm)

Gas

Method

Lower

reflecting

Al

30

0.1

Ar

SP

conductive

layer

method

layer

transparent

ZnO

250

1.0

Ar

SP

conductive

method

layer

Ratio

Tem-

Power

of

per-

fre-

flow

Pres-

ature

Thick

quency

rates

sure

Layer

Material

(° C.)

(μm)

(MHz)

SiH

4

/H

4

(Torr)

Photo-

1st

a-Si:H:P

380

0.04

13.56

0.08

1.0

voltaic

doped

layer

layer

1st i-

μ c-Si:H

400

0.70

500

0.04

0.01

layer

2nd

μ c-

200

0.006

13.56

0.02

1.5

doped

Si:H:B

layer

3rd

a-Si:H:P

220

0.01

13.56

0.08

1.0

doped

layer

2nd i-

a-Si:H

200

0.16

13.56

0.05

1.2

layer

4th

μ c-

160

0.005

13.56

0.02

1.5

doped

Si:H:B

layer

Temper-

ature

Thick

Layer

Material

(° C.)

(μm)

Gas

Method

Upper electrode

ITO

160

0.08

Ar + O

2

SP method

SP method: sputtering

The cross-section of this solar cell was observed by TEM, which indicated that the first i-layer was made in the microcrystalline structure as shown in FIG.

1

B. The surface roughness Ra of the lower conductive layer (the transparent, conductive layer/the reflecting layer) was measured, which showed that the average per 50 μm length was 0.29 μm. The percentage of angles G (each of which is an angle between the normal line to a fine area of the lower conductive layer and the normal line to the principal plane of the substrate) in the range of 15° to 45° both inclusive was calculated. It was 93%. The percentage K of the overall volume of prismatic crystalline grains with the angle F being 20° or less to the overall volume of the first i-layer was 94%.

Comparative Example 2

Several photoelectric conversion elements (Comp. Ex. 2) were fabricated by stacking the third doped layer, the second i-layer, and the fourth doped layer as in Example 2 between the second doped layer and the upper transparent electrode in the solar cell of Comparative Example 1 (Table 1B) having the structure as shown in FIG.

2

. The cross-section of this solar cell was observed by TEM, which indicated that the first i-layer was made in the microcrystalline structure as shown in FIG.

2

. The same measurements and tests as in Example 1 were conducted, which confirmed that the solar cells of Ex. 2 were better than those of Comp. Ex. 2.

Example 3

A long sheet was used as the substrate, and the reflecting layer and the transparent, conductive layer were successively formed thereon by the roll-to-roll method with high productivity. Further, the roll-to-roll method was also employed for forming the photovoltaic layer and the upper transparent electrode. The details thereof will be described.

Apparatus

1000

of

FIG. 10

is a thin film forming apparatus that can make some thin films on the surface of long sheet substrate

1001

with flexibility in a vacuum. Reference numeral

1001

designates the long substrate with flexibility, such as stainless steel,

1008

a delivery roll around which the substrate is wound in a roll form,

1009

a winding roll for winding the substrate thereon, and

1002

a vacuum vessel in which the delivery roll can be fixed. A vacuum pump

1016

such as a rotary pump is connected to the vacuum vessel through a pipe

1018

. Similarly, the winding roll

1009

is fixed in vacuum vessel

1007

, and a vacuum pump is connected thereto.

Connected between the vacuum vessels

1002

and

1007

as shown in

FIG. 10

are a path of the substrate, called gas gates

1021

, and vacuum vessels

1003

,

1004

,

1005

,

1006

for forming the desired thin films by DC magnetron sputtering. Gas inlet pipe

1010

is connected to each gas gate

1021

as illustrated to allow scavenging gas

1011

of Ar or the like to flow into the gas gate, whereby mutual diffusion of gas can be prevented from occurring between the vacuum vessels for forming different thin films. As a result, a good junction can be formed. The gas gates are connected between the vacuum vessels, but the gas gate does not have to be provided between the vacuum vessels if identical thin films are made in consecutive vacuum vessels.

Diffusion pump

1017

is connected through pipe

1019

to each vacuum vessel

1003

,

1004

,

1005

,

1006

, and a vacuum pump such as a rotary pump is further connected through a pipe thereto. Further provided inside each vacuum vessel

1003

,

1004

,

1005

,

1006

are heater

1014

for heating the substrate, target

1023

for forming a desired thin film, electrode

1013

having a built-in magnet, and gas inlet pipe

1020

for introducing gas

1022

for sputtering. DC power supply

1012

is connected to each electrode.

A method for using this apparatus will be described. First, the delivery roll

1008

on which the long substrate with flexibility such as stainless steel is rolled is fixed in the vacuum vessel

1002

, and the leading end of the substrate is guided through the gas gates and vacuum vessels

1003

,

1004

,

1005

,

1006

into the vacuum vessel

1007

and is wound around the winding roll

1009

fixed inside the vacuum vessel

1007

.

Each vacuum pump is actuated to evacuate the inside of each vacuum vessel before the internal pressure of each vacuum vessel becomes several mTorr. Ar gas is introduced through each gas inlet pipe

1010

and desired gas through

1020

, the power supply of each heater is turned on, and the substrate is conveyed in the direction of arrow

1024

. When the temperature of the substrate becomes constant, each DC power supply is turned on to induce plasma

1015

in each vacuum vessel

1003

,

1004

,

1005

,

1006

, thereby forming the desired thin films.

The conveyance is stopped with arrival of the trailing end of the substrate, each DC power supply and each heater power supply are turned off, and the substrate is cooled. When the temperature of the substrate becomes nearly equal to room temperature, each vacuum vessel is made to leak and then the winding roll is taken out.

The reflecting layer and the transparent, conductive layer were continuously made using the stainless steel substrate (SUS 430) 0.15 mm thick by the above method and under the conditions shown in Table 3. The cross-sectional shape of this lower conductive layer (the transparent, conductive layer/the reflecting layer) was observed by SEM, which indicated that the layer had the shape as shown in

FIG. 1A

or

1

B. The average surface roughness Ra per 50 μm length was 0.35 μm. The percentage of angles G in the range of 15° to 45° both inclusive, calculated, was 90%.

Next described in detail is an apparatus for forming the photovoltaic layer on the transparent, conductive layer by the roll-to-roll method. The apparatus of

FIG. 11

is an apparatus for continuously making the photovoltaic layer comprised of six layers on the long substrate, and some of the vacuum vessels are not illustrated in the drawing. Reference numeral

1101

designates the long substrate on which the lower conductive layer was formed,

1108

a delivery roll around which the substrate is wound in a roll form,

1109

a winding roll for winding the substrate, and

1102

a vacuum vessel in which the delivery roll can be fixed. A vacuum pump

1116

such as the rotary pump is connected thereto through pipe

1118

. Similarly, the winding roll

1109

is fixed in the vacuum vessel

1107

, and a vacuum pump is connected thereto. Vacuum vessels

1103

-

a

,

1104

,

1103

-

b

(not illustrated),

1103

-

c

(not illustrated),

1103

-

d

,

1103

-

e

for forming the desired thin films are placed in order between vacuum vessels

1102

and

1107

, and gas gates

1121

are connected between the vacuum vessels. Gas inlet pipe

1110

is connected to each gas gate

1121

as illustrated to allow the scavenging gas

1111

of Ar, H

2

, He, or the like to flow into each gas gate, whereby mutual diffusion of gas can be prevented from occurring between the vacuum vessels for forming different thin films. As a result, the pin junction obtained is very good. The gas gate does not always have to be provided between the vacuum vessels if identical thin films are formed in consecutive vacuum vessels.

The RF plasma enhanced CVD (power frequency 13.56 MHz) can be carried out in vacuum vessels

1103

-

a

,

1103

-

b

,

1103

-

c

,

1103

-

d

,

1103

-

e

. The rotary pump and gas inlet pipe

1120

are connected through pipe

1118

to each of the vacuum vessels, and heater

1114

and RF electrode

1113

are fixed inside each vacuum vessel. RF power supply

1112

is connected to the RF electrode. The high-frequency plasma enhanced CVD (power frequency 150 MHz) can be carried out in the vacuum vessel

1104

. Diffusion pump

1117

is connected through pipe

1119

to the vacuum vessel, and the vacuum pump such as the rotary pump is further connected through a pipe thereto. Further, the gas inlet pipe is connected to the vacuum vessel, and the heater

1117

and high-frequency electrode

1126

are fixed inside. High-frequency power supply

1125

(frequency 150 MHz) is connected to the high-frequency electrode.

A method of use of this apparatus will be described. First, the delivery roll

1108

on which the above stainless steel substrate with the lower conductive layer is rolled is fixed in the vacuum vessel

1102

and the leading end of substrate is guided through each gas gate and each vacuum vessel to the inside of vacuum vessel

1107

and is wound around the winding roll

1109

fixed inside the vacuum vessel

1107

. Then each vacuum pump is actuated to evacuate the inside of each vacuum vessel before the internal pressure of each vacuum vessel becomes several mTorr. H

2

gas is introduced through the gas inlet pipe

1110

and gases for forming the photovoltaic layer through the gas inlet pipes

1120

, each heater power supply is turned on, and the substrate is conveyed in the direction of arrow

1124

. When the temperature of the substrate becomes constant, each RF power supply and the high-frequency power supply are turned on and matching is adjusted to induce the plasma

1115

inside each vacuum vessel, thereby forming the desired thin films. The conveyance is stopped with arrival of the trailing end of the substrate, each RF power supply, each high frequency power supply, and each heater power supply are turned off, and the substrate is cooled. When the temperature of the substrate becomes nearly equal to room temperature, each vacuum vessel is made to leak and the winding roll is taken out. The first doped layer of a-Si:H:P/the first i-layer of μ cSi:H/the second doped layer of μ c-Si:H:B/the third doped layer of a-Si:H:P/the second i-layer of a-Si:H/the fourth doped layer of μ c-Si:H:B were made by the above-described method and under the conditions shown in Table 3.

The upper transparent electrode (ITO) was made continuously on the rolled solar cell thus taken out, using the apparatus of FIG.

10

. On that occasion, the upper transparent electrode of ITO was made on the fourth doped layer in such a manner that the target inside the vacuum vessel

1006

was ITO and that only vacuum vessel

1006

was used without inducing the plasma in the vacuum vessels

1003

,

1004

,

1005

. The conditions for making each layer are shown in Table 3.

TABLE 3

Temper-

Vacuum

ature

Thick

Gas for

vessel

Target

Layer

Material

(° C.)

(μm)

sputtering

Method

1003

Al

Lower

reflecting layer

Al

30

0.15

Ar

SP method

1004

ZnO

conductive

transparent

ZnO

200

0.20

Ar + O

2

SP method

1005

ZnO

layer

conductive layer

ZnO

250

0.50

Ar

SP method

1006

ZnO

ZnO

250

0.50

Ar

SP method

Temper-

Power

Vacuum

ature

Thick

frequency

Pressure

vessel

Layer

Material

(° C.)

(μm)

(MHz)

SiH

4

/H

2

(Torr)

1103-a

1st doped layer

a-Si:H:P

300

0.03

13.56

0.05

1.2

1104

1st i-layer

μc-Si:H

380

0.85

150

0.03

0.03

1103-b

2nd doped layer

μc-Si:H:B

200

0.006

13.56

0.02

0.5

1103-c

3rd doped layer

a-Si:H:P

200

0.02

13.56

0.05

1.2

1103-d

2nd i-layer

a-Si:H

200

0.18

13.56

0.06

1.0

1103-e

4th doped layer

μc-Si:H:B

160

0.005

13.56

0.02

0.5

Temper-

Vacuum

Tar-

ature

Thick

Gas for

vessel

get

Layer

Material

(° C.)

(μm)

sputtering

Method

1006

ITO

upper transparent electrode

ITO

160

0.08

Ar + O

2

SP method

The rolled solar cell taken out was cut in the size of 30×30 cm

2

, then the collector electrode and bus-bar as in Example 1 were attached as shown in

FIG. 1A

, four solar cells are connected in series as shown in

FIG. 4

, and a bypass diode is connected in parallel with each solar cell. Then stacked on a support substrate 0.3 mm thick were EVA, polyamide resin, EVA, nonwoven glass fabric, the solar cells connected in series, nonwoven glass fabric, EVA, nonwoven glass fabric, EVA, nonwoven glass fabric, and fluororesin, and the stack was subjected to heating-vacuum sealing (lamination).

The same measurements and tests as in Example 1 were conducted for the solar battery module (Ex. 3) fabricated as described above in the size of 35×130 cm. In either one of the initial characteristics, the torsion test, and the hailstorm test, the solar cell module Ex. 3 was better than the solar cell of Ex. 1. The outdoor exposure test was conducted while the solar cell module of Ex. 3 was placed outdoors for three months. Little change was observed in its appearance, and a drop of photoelectric conversion efficiency was about 5%.

It was confirmed that the photovoltaic module of the present invention had excellent characteristics.

Example 4

The solar cell (Ex. 4) was made in the same manner as in Example 1, except that the thickness of the first i-layer in Example 1 was changed to 2 μm. When the cross-section was observed by TEM, the structure of the first i-layer was found to be as shown in

FIG. 1A

or

1

B. The same measurements and tests as in Example 1 were conducted, which showed that the solar cell of Ex. 4 was as good as the solar cell of Ex. 1.

Example 5

The solar cell in which the lower conductive layer was a single layer was made as another example. The lower conductive layer was a layer of silver 0.5 μm thick and was made by sputtering. The surface of the layer was roughened (or textured) by keeping the temperature of formation at 350° C. The cross-section was observed to count the percentage of angles G (each of which is an angle between the normal line to the fine area of the lower conductive layer and the normal line to the principal plane of the substrate) in the range of 15° to 45° both inclusive, and the percentage was 91%. Several solar cells Ex. 5 of

FIG. 1A

were made by forming the same photovoltaic layer, the upper transparent electrode, and the collector electrode as in Example 1, on the lower conductive layer. The same measurements and tests as in Example 1 were conducted, which showed that the solar cells of Ex. 5 were as good as the solar cell of Ex. 1.

Example 6

The solar cell of

FIG. 1B

with the photovoltaic layer of

FIG. 5

in which the first doped layer was of the stacked structure of a-Si:H:P/μ c-Si:H:P was made as another example. The solar cell (Ex. 6) was made in the same manner as in Example 2, except that the first doped layer of Example 2 was changed to that of a-Si:H:P/μ c-Si:H:P. The same measurements and tests as in Example 1 were conducted, which showed that the solar cell of Ex. 6 was as excellent as the solar cell of Ex. 2.

Number	Name	Date
5221365	Noguchi et al.	Jun 1993
5282902	Matsuyama	Feb 1994
5453135	Nakagawa et al.	Sep 1995
5486237	Sano et al.	Jan 1996
5510285	Kim	Apr 1996
5549763	Sano et al.	Aug 1996
5585653	Nakashiba	Dec 1996
5677236	Saitoh et al.	Oct 1997

Photoelectric conversion element

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (8)

Foreign Referenced Citations (1)

Non-Patent Literature Citations (6)

Entry
Meier, J., et al., “Intrinsic Microcrystalline Silicon (uc-Si:H)-A Promising New Thin Film Solar Cell Material”, 1994 IEEE First World Conference on Photovoltaic Energy Conversion, vol. 1, p. 409 (1994).
M.B. Schubert et al., “Optimum Front Contact and Growth Conditions for Microcrystalline Silicon Solar Cells from Hot-Wire CVD”, 25th IEEE Photovoltaic Spec. Conf. Proc., pp. 1081-1084 (May 1996).
Patent Abstracts of Japan, E-1578, Apr. 15, 1994, p.7 (corresponds to JP 6-104476).
Patent Abstracts of Japan, E-511, Jan. 8, 1987, p.78 (corresponds to JP 62-2575).
Patent Abstracts of Japan, E-893, Dec. 7, 1989, p.141 (corresponds to JP 1-303752).
Patent Abstracts of Japan, E-430, Apr. 17, 1986, p. 155 (corresponds to JP 61-75559).